Unitary resistor and shunt

ABSTRACT

A method of producing a distributed shunt for resistor film. The steps of this method comprising the selection of a conductive material whose sintering temperature is substantially lower than the sintering temperature of the resistive material; locating the conductive material in single or segmented form on the surfade of the resistive material intermediate end portions of the latter and firing the conductive material on the resistive material at the sintering temperature of the conductive material whereby the tendency to diffusion between said conductive and resistive materials is minimized and the resistivity of the resistive material is reduced while maintaining substantially constant the temperature coefficiient of resistivity and stability of the resistive material.

United States Patent [1 1 Schebalin [451 Sept. 3, 1974 UNITARY RESISTORAND SHUNT [75] Inventor: Sergei Schebalin, Ambler, Pa.

[73] Assignee: Honeywell Inc., Minneapolis, Minn.

[22] Filed: June 12, 1972 [21] Appl. No.: 261,971

Related US. Application Data [62] Division of Ser. No. 122,777, March10, 1971, Pat.

[52] US. Cl 117/212, 117/217, 117/227, 333/49 [51] Int. Cl 344d l/18,HOlc 13/00 [58] Field of Search 117/212, 217, 227; 338/49 [56]References Cited UNITED STATES PATENTS 3,274,669 9/1966 Place 117/2123,381,255 4/1968 Cobb 117/212 3,567,507 3/1971 'Youmans. 3,699,65010/1972 .IIIA, l

Cocca. 117 212 Primary Examiner-Leon D. Rosdol AssistantExaminer-Michael F. Esposito Attorney, Agent, or FirmArthur H. Swanson;Lockwood D. Burton; J. Shaw Stevenson [5 7 ABSTRACT and the resistivityof the resistive material is reduced while maintaining substantiallyconstant the temperature coefficiient of resistivity and stability ofthe resistive material.

2 Claims, 3 Drawing Figures r i 0/, i 1

application.

UNITARY RESISTOR AND SHUNT This application is a divisional applicationof Ser. No. 122,777 filed on Mar. 10, l971,'now US. Pat. No. 3,743,997.

It is an object of the present invention to provide a unique resistorfilm and shunt and the method by which this unit can be manufactured.

More specifically, it is another object of the invention to provide aresistor film distributed shunt for an electrical circuit that employsconductor material fired on a resistor film in a characteristic manner.

It is still another object of the present invention to provide adistributed shunt of the aforementioned type for a resistor film thatrequires less space than conventional shunts since it eliminates therequirement for an external resistance and allows all of its shuntingaction to take place within a single resistor.

Another object of the invention is to provide a resistor film such ase.g. that which is disclosed in my copending patent application Ser. No.120,199 filed Mar. 2, 1971, now US. Pat. No. 3,788,891 and its relateddivisional application, Ser. No. 334,956, filed Mar. 26, I973. withcharacteristically spaced apart conductive material fired thereon andthereby provides a method by which the resistivity of the resistordescribed in the aforementioned referred to application can be loweredwithout incurring any change in the temperature coefficient ofresistivity and its stability.

Another object of the present invention is to provide a uniquedistributed shunt ofv the aforementioned type having an array ofpolka-dots printed on a resistor film and which may have open portionspassing therethrough between the rows of dots which form the array andthereby be able to create an extremely lightweight resistor.

More specifically it is another object of the present inventiontoprovide the aforementioned resistor with a number of small spots ofdisc shape conductive material that are spaced from one another in acharacteristic pattern.

Another object of the invention is to screen conductive ink spots ontothe aforementioned resistor so that they can be jointly fired with theresistor at the same time and at the same temperature as that describedfor the two terminal conductors set forth in my copending It is anotherobject of the present invention to provide a means of reducing the sizeof presently available characterized resistor film or wire woundvariable resistors by providing a modified form of the aforementioneddistributed shunt in which a desired diminishing concentration of discshaped conductors are formed along the length of the resistor.

A better understanding of the invention may be had from the followingdetailed description when read in connection with the accompany drawingin which:

FIG. 1 is a cross-sectional view taken through the resistor film andthrough the unique array of conductive dots which are fired onthisresistor.

FIG. 2 is a detailed plan view of a preferred form of the thick filmresistor distributed shunt showing how conductors formed in polka-dotpattern are printed on the thick film resistors shown in FIG. 1 and FIG.3 shows how a variable resistor can be formed by the addition of arraysof conductive'dots of increasing density between one end of the resistorand another.

FIG. 1 shows a resistor film 10 that has been selected from any one of anumber resistor ink mixes for firing onto a non-electrically conductivesubstrate 12 at 1000C. The material that is employed for the substrateis an aluminum oxide that is preferably ninety six percent pure. Oneexample of a positive coefficient of resistivity resistor ink that canbe used to make part of the mix for resistor 10 is percent by weightruthenium, 20 percent by weight ruthenium oxide, R 0 and the remainder40 percent by weight formed from glass frit. An example of a negativecoefficient of resistivity resistor ink that can be used to make theremaining part of the desired mix for resistor 10 is comprised ofsubstantially 40 percent by weight of R O 20 percent by weight of R and40 percent by weight of glass frit.

FIG. 1 also shows a pair of conductors l4, l6 fired onto associatedopposite ends of the resistor 10 for connecting the resistor toterminals 18, 20.

FIGS. 1 and 2 show disc shaped conductors e.g. 22, 24, 26 and 28 whichprotrude from the upper surface of the resistor 10.

These conductors are preferably made of the same silver-glass conductiveinkmaterial as the terminal con ductors set forth in my copendingapplication Ser. No. 120,199 filed Mar. 2, 1971, now US. Pat. No.3,788,891 and its related divisional application, Ser. No. 334,956,filed Mar. 26, 1973. It should be understood that although the resistor10 is made into a distributed shunt by the firing on of the polka-dotsin the preferred fashion shown in F IG.2 other forms of conductors suchas strips, squares, etc. could be used for this purpose.

The polka-dot arrangement is considered the preferable form because theyinsure that most uniform distribution ofthe conductor material over theresistor. It should be understood that the resistor 10 is first I firedat 1,000C onto the electrically non-conductive substrate 12. Theconductive disc, for example 22, 24, 26, and 28, and the other remainingconductive discs shown in a polka-dot fashion in FIG. 2 are thereafterjointly fired along with the terminals conductors l4, l6 and theresistor 10 at 550C.

The aforementioned unique firing method allows the conductive discs, forexample 22, 24, 26, and 28, to be fired onto the resistor 10 with annegligible amount of diffusion taking place between these conductivedisc and their associated resistor 10. The polka-dot pattern has theadvantage over the other'aforementioned conductors, in that any smallamount of diffusion that occurs between a conductive disc 22, 24, 26, or28 and the resistor 10 will always be uniform.

It is to be understood that the addition of the conductive discs such asthe conductors 22-28 shown in FIGS. 1 and 2 to the outer surface of theresistor 10 provides a way of keeping its size, such as its width andlength I of an abnormally small dimension. These conductors e. g. 22-28also retain the basic parameters such as temperature coefiicient ofresistivity and the stability of resistor 10 substantially constant andat the same time provide a method to decrease by as much as ten theresistivity of the resistor 10.

- If it is desired to use the resistor 10 and its associated disc shapedconductive dots e.g. 22, 24, 26 28 etc. as a resistance distributedshunt in a miniaturized printed circuit the arrayof conductive discsformed thereon can be covered by means of a flexible material such as aflexible silicone polmer and a second hard outer covas the resistor andthe terminal conductors are covered in my copending application Ser. No.334,95 6. This encapsulating structure will protect the resistor fromambient air, water vapor, water and hydrogen sulfide (H S) and ambienttemperature that may vary from the standard reference level of C i 50 Cso that no more than 121% change in value of the resistor can oc- CUI'.

In another application it may be desirable, as is shown in'FIG. l, toemploy the resistor 10 and its associated disc shaped conductive dots asa shunted slide wire along which a metallic wiper and a support member32 for same can be moved in the direction of the arrows along thesurface 32. The wiper 30 can be of a multiple contacting type in whichsome of contacts formed by wiper 30 in contact with some of theconductive dots 22, 24, 26, or 28 etc. as it is moved along the topsurface of resistor 10. This will be so because the multiple fingersarrangement of this wiper 30 will allow it to always contact some of thedots in a row of dots as it travels across the dots 22-28 on theresistor 10 because of the polka-dot pattern of these dots. The distancebetween each row of dots is 0.20 inches, the distance betweeneach dot inany row is .030 inches and the diameter of the each conductive dot is.020 inches. It can therefore be seen that contacts formed by the wipers30 are of sufficient width that some one or more of them will always bein contact with at least one half of one of the dots of each row alongwhich it is brought into contact.

The height of the dots e.g. 22-28 above the surface of the resistor 10is .00035 inches.

One thumb rule method of calculating the amount of resistance which isaffored by a resistor having equally distributed conductive dots, can bederived as follows:

I R withdots=R no dotsA AA/A+AA K wherein A A is equal to the total areaof deposited evenly distributed dots.

A is equal to the total area of the resistorbefore the dots are firedthereon and K is a factor which for the distribution shown in FIG. 2 isequal to 2.

From the aforementioned it can be seen that the conductive dots such asdots 22-28, provide a precise way of causing electrical fields to movein a arcuate fashion between adjacent pairs of dots and thereby affectan internal shunting action.

FIG. 3 shows a resistor 10 mounted on a substrate 12. The resistor 10 asshown in FIG. 3 has its end portions connected to terminals 18-20 bymeans of conductive materials l4, 16 in the same manner as that shown inFIG. 1. FIG. 3 differs from FIGS. 1 and 2 in the manner in which thedots shown in FIG. 3 are positioned on the resistor 10. For example, thedots 36, 38, 40 that are located near the left-end of the resistor arewidely spaced apart from one another. The conductive dots 42, 44, 46mid-way between the ends of the resistor are spaced closer to theiradjacent dots than the adjacent.

dots with which dots 36, 38, 40 are associated and the spacing of theconductor dots 48, 50, 52 are spaced in a still more closely relateddense fashion with their adjacent dots that they are associated than anyother preceeding group of dots.

With the aforementioned construction shown in FIG. 3 it can be seen thata much greater degreeof shunting of the aforementioned electrical fieldwill take place between the dots near conductor 16 than those nearconductor 12.

It can also be seen that as the multipoint contacting wiper 30,previously described under the description of FIG. 1, is moved along theresistor 10 in a left to right direction that a characterized decreasingresistance will be encountered. It should be understood that otherdifferent arrays and shapes of conductive material can be employed forthose shown in FIG. 3 in order to provide either a characteristicresistor per se or an adjustable resistor for a circuit that is employedas a slidewire along which a wiper 30 can be moved.

From the aforementioned description it can beseen that a resistor filmhas been provided which has conductive dots fired onto its outer surfaceso that a distributed shunt is provided within the resistor so that theresistivity of the resistor can be reduced by as much as a factor of tenwithout changing its size and without changing its basic parameters suchas its temperature coefficient resistivity and stability.

Although not shown in the drawing it should be understood that aperturescan be formed in the resistor 10 between the conductive dots, e.g. 22-28when an extremely light weight resistor is desired.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows: V

l. The method of producing a distributed shunt for resistor filmcomprising the steps of selecting a silverglass conductive material anda ruthenium-ruthenium oxide-glass frit resistive material whichconductive material has a sintering temperature substantially lower thanthe sintering temperature of said resistive material, locating saidconductor material on said resistive material intermediate end portionsof the latter, and firing the said conductive material on said resistivematerial at the sintering temperature of said conductive materialwhereby the tendency to diffusion between said conductive and resistivematerials is minimized and the resistivity of said resistive material isreduced while maintaining substantially constant the temperaturecoefficient of resistivity and stability of said resistive material.

2. The method of producing a distributed shunt for resistor film,comprising the steps of firing a rutheniumruthenium oxide-glass fritresistor material onto an electrically non-conductive substrate at thesintering temperature of approximately 1000 degrees C of said resistivematerial, and thereafter firing silver-glass conductive material insegmented form on the surface of said fired resistive materialintermediate end portions of the latter, said second firing being at thesintering temperature of approximately 550 degrees C of said conductivematerial, whereby the tendency to diffusion between said conductive andresistive materials is minimized and the resistivity of said resistivematerial is re duced due to the shunting effect of said conductivematerial on said resistive material, and whereby the temperaturecoefficientof resistivity and stability of said resistive material ismaintained substantially constant. =l

2. The method of producing a distributed shunt for resistor film,comprising the steps of firing a ruthenium-ruthenium oxide-glass fritresistor material onto an electrically non-conductive substrate at thesintering temperature of approximately 1000 degrees C of said resistivematerial, and thereafter firing silver-glass conductive material insegmented form on the surface of said fired resistive materialintermediate end portions of the latter, said second firing being at thesintering temperature of approximately 550 degrees C of said conductivematerial, whereby the tendency to diffusion between said conductive andresistive materials is minimized and the resistivity of said resistivematerial is reduced due to the shunting effect of said conductivematerial on said resistive material, and whereby the temperaturecoefficient of resistivity and stability of said resistive material ismaintained substantially constant.